Outdated/wrong docs docs

[Tobbeman]

The docs in db/deyval/etcd refer to a function which allow use to load a config using a filepath https://github.com/ligato/cn-infra/blob/master/db/keyval/etcd/doc.go#L29

The function in question takes another input however https://github.com/ligato/cn-infra/blob/master/db/keyval/etcd/bytes_broker_impl.go#L57